1. Field of the Invention
The present invention particularly relates to a driving apparatus having an oscillating internal meshing planetary gear structure as its speed change mechanism, such as a geared motor.
2. Description of the Related Art
Conventionally, oscillating internal meshing planetary gearing is widely known which has an internal gear and an external gear internal meshing with the internal gear, the center axis of the internal gear lying inside the periphery of the external gear [the gearing corresponding to International Patents Classification (IPC) F16H 1/32].
FIG. 22 shows an example of a geared motor that has conventional oscillating internal meshing planetary gearing of this type as its reduction gear unit, which is described in Japanese Patent Laid-Open Publication No.Hei 5-231482. This geared motor 1 includes the above-mentioned reduction gear unit (oscillating internal meshing planetary gear unit) 2 and a motor unit 3 connected and integrated with each other.
The reduction gear unit 2 has a casing 51 which is composed of a central casing 52 disposed at the axial center, a joint casing 53 on the side closer to the motor unit 3, and a front casing 54 on the side opposite from the motor unit 3. The motor unit 3 has a casing 55 which is composed of a cylindrical casing 56 having a stator and the like arranged inside, the joint casing 53 on the side closer to the reduction gear unit 2, and a rear cover 57 on the side opposite from the reduction gear unit 2. Here, the above-mentioned joint casing 53 comprises both parts of the casings 51 and 55 for the units 2 and 3. Accordingly, the units 2 and 3 are integrally connected with each other through the joint casing 53.
The reduction gear unit 2 has first and second shafts 11 and 12 serving as input and output shafts, respectively. Both the shafts are aligned on the center axis L of the unit. The first shaft 11 is disposed on one axial end of the reduction gear unit 2. The second shaft 12 is on the other axial end of the reduction gear unit 2.
Two eccentric bodies 13a and 13b are fitted on the outer periphery of the first shaft 11 so as to axially adjoin each other with a given phase difference therebetween (180xc2x0, in this example). These eccentric bodies 13a and 13b make rotations together with the first shaft 11. The respective centers of the eccentric bodies 13a and 13b are a given eccentricity off the axis of the first shaft 11. External gears 15a and 15b are fitted onto the outer peripheries of the eccentric bodies 13a and 13b via bearings 14a and 14b, respectively.
The plural rows of external gears 15a and 15b fitted on the eccentric bodies 13a and 13b are provided with a plurality of inner pin holes 16a and 16b, respectively. Inner pins 17 are fitted to the inner pin holes 16a and 16b with some play.
The external gears are provided in two (in plural rows) mainly for the sake of enhancing the transmission capacity, maintaining the strength, and keeping the rotational balance.
On the outer peripheries of the external gears 15a and 15b are provided outward teeth each having a trochoidal tooth profile or a circular arc tooth profile. These outward teeth come into internal mesh with an internal gear 20 that is provided concentrically with the first shaft 11. The internal gear 20 is integrally formed on the inner periphery of the central casing 52. Each inward tooth of the internal gear 20 is formed with an outer pin 21 held on the inner periphery of the central casing 52.
The result is that the reduction gear unit 2 is characterized by having the internal gear 20 and the external gears 15a, 15b internally meshing with the internal gear 20, the center of the internal gear 20 lying inside the peripheries of the external gears 15a, 15b (the characteristic prescribed in IPC F16H 1/32).
The two external gears 15a and 15b are interposed between a pair of support carriers 23 and 24. These carriers 23 and 24 are rotatably supported by bearings 31 and 32 fitted to the inner peripheries of the joint and front casings 53 and 54, respectively. The carriers 23 and 24 are also integrally connected with each other by a plurality of carrier pins (coupling pins) 25 and spacers 26 piercing through the external gears 15a and 15b. 
The inner pins 17, fitted to the inner pin holes 16a and 16b in the above-mentioned external gears 15a and 15b with some play, are connected at both ends with the carriers 23 and 24 on both sides so as to be capable of sliding rotations. This allows only the rotational components of the external gears 15a and 15b to be transmitted through the inner pins 17 to the carriers 23 and 24 on both the sides.
The carrier 23 closer to the motor unit 3 is of annular shape having a center hole 23a. One end of the first shaft 11 lies inside the center hole 23a so that the end can be coupled to a motor shaft 61.
The other carrier 24 is integrally formed on the base of the second shaft 12, and has a recess 24a into which the other end of the first shaft 11 is inserted. A bearing 33 is fitted to the inner periphery of the central hole 23a in the carrier 23, and a bearing 34 is fitted to the inner periphery of the other carrier 24. The first shaft 11 is rotatably supported by the bearings 33 and 34.
The motor shaft 61 of the motor unit 3 is supported at its rear end by a bearing 62 and at its front end by a bearing 63. The bearings 62 and 63 are fitted to the rear cover 57 and the joint casing 53, respectively. Here, the motor shaft 61 is aligned to be coaxial with the center axis L of the reduction gear unit 2.
The extremity of the motor shaft 61, projected outward from the front-side bearing 63, is inserted into the reduction gear unit 2. Within the center hole 23a in the carrier 23 of the reduction gear unit 2, the extremity is coupled to the end of the first shaft 11 mentioned above via a coupling 70.
In this case, splines are formed in the inner periphery of the coupling 70 and the outer peripheries of both shafts 11 and 61 so that the shafts 11 and 61 come into spline connection with each other through the coupling 70. Here, the splines establish the floating connection between the first shaft 11 and the motor shaft 61 while allowing relative radial play therebetween.
Now, description will be given of the operation of this geared motor.
In the geared motor 1 of such constitution, one rotation of the first shaft 11 coupled to the motor shaft 61 makes one rotation of the eccentric bodies 13a and 13b. This one rotation of the eccentric bodies 13a and 13b urges the external gears 15a and 15b to oscillate and rotate about the first shaft 11. However, since their free rotations on the axis are restricted by the internal gear 20, the external gears 15a and 15b almost exclusively make oscillations while internal meshing with this internal gear 20 (this is a characteristic of speed reduction structures of this type).
Now, assuming that the number of teeth on the respective external gears 15a, 15b is N and the number of teeth on the internal gear 20 is N+1, the difference between the numbers of teeth is xe2x80x9c1.xe2x80x9d On that account, each rotation of the input shaft 1 shifts (rotates) the external gears 15a and 15b by the amount corresponding to one tooth with respect to the fixed internal gear 20. This means that one rotation of the first shaft 11 is reduced to xe2x88x921/N rotations of the external gears 15a and 15b. 
The oscillating components in the rotations of the external gears 15a and 15b are absorbed by the clearances between the inner pin holes 16a, 16b and the inner pins 17. Thus, only the rotational components are transmitted via the inner pins 17 to the carriers 23 and 24, and then to the second shaft 12.
This consequently achieves speed reduction of xe2x88x921/N in reduction ratio (here, the negative sign represents a reverse rotation).
Next, description will be directed to another conventional example.
FIGS. 23 and 24 show an example of a conventional geared motor described in Japanese Patent Laid-Open Publication No.Hei 10-299841. This geared motor 500 uses an oscillating internal meshing planetary gear structure of so-called power-distributed shaft type. This internal meshing planetary gear structure comprises a first shaft 502, power-distributed shafts 503, eccentric bodies 504, external gears 505, an internal gear 506, and a second shaft 507. The first shaft 502 is to be coupled to an external motor shaft 501. The plurality of power-distributed shafts 503 are arranged on the circumference of a circle concentric with the first shaft 502, and make revolutions in response to the first shaft 502. The eccentric bodies 504 are arranged on the plurality of power-distributed shafts 503 on a one-on-one basis. The external gears 505 are fitted on the eccentric bodies 504 so as to be capable of eccentric rotations with respect to the first axis 502. The internal gear 506 is arranged to be concentric with the first axis 502. The above-described external gears 505 come into internal mesh with the internal gear 506 while making the eccentric rotations with respect to the first shaft 502. The second shaft 507 is coupled with the plurality of power-distributed shafts 503. In this internal meshing planetary gear structure, the eccentric bodies 504 are interposed between a pair of support carriers 523 and 524, and the power-distributed shafts 503 are rotatably supported by the carriers 523 and 524. In addition, the above-mentioned first shaft 502 is provided with a sun roller 511. A plurality of power-distributed rollers 512 for making external contact with the sun roller 511 are put into spline connection with the plurality of power-distributed shafts 503 on a one-on-one basis. Around these plurality of power-distributed rollers 512 is arranged a press-contact ring 513 which has an inner diameter somewhat smaller than the sum of the diameter of the above-mentioned sun roller 511 and the value twice the diameter of the power-distributed rollers 512. The power-distributed rollers 512 make internal contact with the press-contact ring 513. Here, the press-contact ring 513 has the function of creating contact forces between the sun roller 511 and the power-distributed rollers 512, which is different from that of the ring in a simple planetary structure.
This kind of gear structures as shown in FIGS. 22 and 23 are divided into two types: namely, a type in which external gears make oscillating rotations with respect to internal gears as described above, and the contrasting type in which internal gears make oscillating rotations with respect to external gears.
By the way, with the recent development of industries, the increasing variety of user needs has grown the demand for driving apparatuses which can offer yet higher reduction ratios (for example, reduction ratios equal to or higher than 1/200) with compact configurations. FIG. 28 shows a driving apparatus of two stage type, having been proposed in response to these needs.
This driving apparatus 1001 has an additional reduction mechanism unit interposed between its reduction mechanism unit and drive unit to make higher reduction ratios up to about 1/1000 attainable. Specifically, the driving apparatus 1001 comprises: a drive unit (motor) 1002 for generating rotational power; a first reduction mechanism unit 1004 coupled to the drive unit for rotational power transmission; and a second reduction mechanism unit 1006 of internal meshing planetary gear structure, coupled to the first reduction mechanism unit for rotational power transmission.
The second reduction mechanism unit 1006 in the driving apparatus 1001 has a first shaft (input shaft) 1011 to be coupled to the first reduction mechanism unit 1004, and a second shaft 1012 arranged to be coaxial with the first shaft 1011 to make the output shaft. Two eccentric bodies 1013a and 1013b are fitted on the outer periphery of the first shaft 1011 so as to axially adjoin each other with a given phase difference therebetween (180xc2x0, in this example) These eccentric bodies 1013a and 1013b make rotations together with the first shaft 1011. The respective centers of the eccentric bodies 1013a and 1013b are a given eccentricity off the axis of the first shaft 1011. External gears 1015a and 1015b are fitted on the outer peripheries of the eccentric bodies 1013a and 1013b via bearings 1014a and 1014b, respectively.
The plurality of external gears 1015a and 1015b fitted on the eccentric bodies 1013a and 1013b are provided with a plurality of inner pin holes 1016a and 1016b, respectively. Inner pins 1017 are fitted to inner pin holes 1016a and 1016b with some play.
The external gears are provided in two (in plural rows) mainly for the sake of enhancing the transmission capacity, maintaining the strength, and keeping the rotational balance. The plural-row configuration is particularly preferable when this structure is applied to the subsequent stage of a two-stage type driving apparatus as in this example. The reason for this is that the transmission capacity (transmission torque) increases on the subsequent stage.
On the outer peripheries of the external gears 1015a and 1015b are provided outward teeth each having a trochoidal tooth profile or a circular arc tooth profile. These outward teeth come into internal mesh with an internal gear 1020 which is provided concentrically with the first shaft 1011. The internal gear 1020 is integrally formed on the inner periphery of the casing 1051. Each inward tooth of the internal gear 1020 is formed with an outer pin 1021.
The result is that the second reduction mechanism unit 1006 is characterized by having the internal gear 1020 and the external gears 1015a, 1015b internally meshing with the internal gear 1020, the center of the internal gear 1020 lying inside the peripheries of the external gears 1015a, 1015b (the characteristic prescribed in IPC F16H 1/32).
The casing 1051, explained particularly, is composed of a central casing 1052, a joint casing 1053 on the side close to the drive unit 1002, and a front casing 1054 arranged on the side opposite from the joint casing 1053. Thus, this casing 1051 accommodates the second reduction mechanism unit 1006.
The two external gears 1015a and 1015b are interposed between a pair of carriers (supporting carriers) 1023 and 1024. These carriers 1023 and 1024 are rotatably supported by two bearings 1031 and 1032 fitted to the inner periphery of the casing 1051. Besides, the carriers 1023 and 1024 are integrally connected with each other by a plurality of carrier pins (coupling pins) 1025 and spacers 1026 piercing through the external gears 1015a and 1015b. 
The inner pins 1017, fitted to the inner pin holes 1016a and 1016b in the external gears 1015a and 1015b with some play, are supported at both sides by the pair of carriers 1023 and 1024 so as to be capable of sliding rotations. This allows only the rotational components of the external gears 1015a and 1015b to be transmitted to the carriers 1023 and 1024.
The carrier 1023 closer to the drive unit 1002 is of annular shape having a center hole 1023a. One end of the first shaft is supported by the center hole 1023a via a bearing. The other shaft end is supported by another bearing fitted into the carrier 1024 on the opposite side. In short, the first shaft 1011 is rotatably accommodated in between the pair of carriers 1023 and 1024.
In this second reduction mechanism unit, one rotation of the first shaft 1011 causes the rotation of both the eccentric bodies 1013a and 1013b. This urges the external gears 1015a and 1015b to oscillate and rotate about the first shaft 1011. However, since their free rotations are restricted by the internal gear 1020, the external gears 1015a and 1015b almost exclusively make oscillations while internally meshing with the internal gear 20.
Assuming that the number of teeth on the respective external gears 1015a, 1015b is N and the number of teeth on the internal gear 1020 is N+1, then the difference between the numbers of teeth is xe2x80x9c1.xe2x80x9d Thus, each rotation of the first shaft 1011 shifts (rotates) the external gears 1015a and 1015b by the amount corresponding to one tooth with respect to the fixed internal gear 20. The result is that one rotation of the first shaft 1011 is reduced to xe2x88x921/N rotations of the external gears 1015a and 1015b. 
The oscillating components in the rotations of the external gears 1015a and 1015b are absorbed by the clearances between the inner pin holes 1016a, 1016b and the inner pins 1017. On that account, only the rotational components are transmitted via the inner pins 1017 to the carriers 1023 and 1024, and finally to the second shaft 1012.
This consequently achieves speed reduction of xe2x88x921/N in reduction ratio (the negative sign represents a reverse rotation).
In this driving apparatus 1001, the first reduction mechanism unit 1004 also uses an oscillating internal meshing planetary gear structure, and has almost the same configuration as that of the second reduction mechanism unit 1006. For the sake of avoiding repetitive descriptions, like parts or members in this diagram are therefore designated by like reference numerals having the same lower two digits, and their constitutional, operational, and other detailed descriptions will be omitted here.
The first reduction mechanism unit 1004 is different from the second reduction mechanism unit 1006 chiefly in the provision of a single (singular row of) external gear 1315. The reason for the difference seems to be that the preceding stage is smaller in transmission capacity (transmission torque) as compared to the subsequent stage, so that even a single external gear can well satisfy the strength and other requirements.
A carrier 1324 on the output side of the first reduction mechanism unit 1004 is coupled to the first shaft 1011 of the second reduction mechanism unit 1006 by means of a spline structure. A first shaft 1311 of the first reduction mechanism unit 1004 is coupled to a drive shaft 1061 of the drive unit 1002.
The casing 1351 for accommodating the first reduction mechanism unit 1004 is composed of a central casing 1352, a joint casing 1353 on the side closer to the drive unit 1002, and the joint casing 1053 on the side closer to the second reduction mechanism unit 1006. Hence, it is the joint casing 1053 that integrally connects the first and second reduction mechanism units 1004 and 1006, and comprises parts of both the casings 1051 and 1351.
In the driving apparatus 1001 of the above-described constitution, the rotational power from the drive unit 1002 is decelerated in two steps by the first and second reduction mechanism units 1004 and 1006 both of oscillating internal meshing planetary gear structure, and then output though the second shaft 1012.
By the way, these conventional examples have been facing a common problem. That is, a reduction gear unit using this kind of internal meshing planetary gear structure, in which the external gears (or internal gear) make(s) relative oscillating rotations with respect to the mating gear(s), indeed has an advantage in that higher reduction ratios can be obtained from the simple, compact, high-rigiditied structure. However, such a reduction gear unit inevitably causes a high-noise problem due to the configuration that the external gears (or internal gear) make(s) oscillations while meshing with the mating gear(s).
In particular, since a reduction gear unit is connected to another external unit in actual use, these units produce resonance with each other to cause a problem of yet higher noise production.
For example, when the reduction gear unit is combined with a motor to constitute a geared motor as described above, the vibrations produced from the reduction gear unit vibrate the motor coupled to the unit. These vibrations are then combined with the vibrations generated by the motor itself to produce complex resonance. Moreover, these vibrations are sometimes returned to the reduction gear unit to generate more complex resonance, possibly causing the entire geared motor to produce extremely high noise.
In this regard, the geared motors in the above examples have already been provided with prevention measures against the resonance between the motor unit and the reduction gear unit(s) For example, in the example of FIG. 22, the motor shaft 61 and the first shaft 11 were put into floating connection with each other via the spline-type coupling 70 to block the mutual transmission of vibrations between the motor unit 3 and the reduction gear unit 2.
However, simply establishing a floating connection through the intervention of the coupling 70 could not achieve very successful suppression against the mutual transmission of the vibrations, failing to offer a sufficient noise reduction effect.
Besides, the geared motor of FIG. 23, using the internal meshing planetary gear structure of power-distributed shaft type, was actually operated and found that it also failed to offer a noise reduction effect as high as expected. The cause for this seems to be as follows:
In this power-distributed-shaft-typed structure, the respective power-distributed shafts 503 are subjected to vibrations and flexure accompanying the oscillating movements of the external gears 505. This inevitably increases the possibility that the power-distributed shafts 503 be vibrated or deformed (bent) under the loads from the external gears 505. Meanwhile, this geared motor still arranges on the power-distributed shafts 503 the power-distributed rollers 512 which are in press contact with the sun roller 511. As a result, the vibrations and deformations of the power-distributed shafts 503 are directly transferred to the power-distributed rollers 512 and then to the sun roller 511, whereby the effect obtained from the use of the friction rollers, of blocking the vibration transmission, is hampered from functioning successfully. In other words, the assignable cause seems to be the configuration that the rollers 512 suitable for high-speed, low-torque power transmission are directly arranged on the power-distributed shafts 503 which undergo the direct influence of the deformation accompanying the load transmissions in the internal meshing planetary gear structure.
In any case (regardless of the cause), the above-described conventional art, despite the incorporation of frictional rollers, ended up failing to achieve such a profound noise-improving effect as would renew the common knowledge.
In the meantime, the driving apparatus 1001 shown in FIG. 28 was capable of achieving extremely high reduction ratios by virtue of the first and second reduction mechanism units 1004 and 1006 both of oscillating internal meshing planetary gear structure. In this respect, the driving apparatus 1001 well satisfied the wide needs of the market. In other words, a feature of this driving apparatus 1001 was that the rotational power from the drive unit 1002 can be transmitted to the second shaft 1012 of the second reduction mechanism unit 1006 as maintained in coaxiality to offer extremely high output.
The driving apparatus 1001, however, was configured so that the new central and joint casings 1352 and 1353 were interposed between the second reduction mechanism unit 1006 and the drive unit 1002 to accommodate the first reduction mechanism unit 1004. This configuration caused a great axial extension of the entire apparatus and ended up with considerably high manufacturing costs.
Even in this driving apparatus shown in FIG. 28, both the first and second reduction mechanism units 1004 and 1006 were of reduction gear structures including gears (external internal gears). Therefore, when coupled to each other, these units produced a problem of greatly-increased noises. An assignable cause appears to derive from the configuration of simply coupling (linking) the casings 1051 and 1351 which have an internal space independent of each other. Here, noises inside the respective casings are resonated and amplified in both the internal spaces. Another cause appears to consist in that: like the examples of FIGS. 22 and 23 described before, the drive units 1002 and two reduction mechanism units 1004 and 1006, each having one or more peak frequencies different from those of the others, are coupled with one another to produce complex resonance phenomena.
By the way, the approaches to a two-stage reduction type attaining higher reduction ratios, other than the driving apparatus 1001 described above, seems to include the conversion of the first reduction mechanism unit into a parallel axis gear structure having spur gears in combination.
To attain a high reduction ratio, however, this parallel axis gear structure requires a greater center distance between the input-side gear (pinion) and the output-side gear so as to establish a larger difference in the number of teeth between the meshing gears. Then, in response to the center distance, the entire driving apparatus is expected to be greater in radial dimension (along with axial dimension). Besides, in order to make the drive unit (motor) and the output shaft coaxial with each other, the first reduction mechanism unit itself requires two stages of gears (three stages, for the entire apparatus) to correct the deviation of the shaft center, inevitably causing axial extension of the apparatus.
The present invention has been achieved in view of the foregoing problems. It is thus an object of the present invention to provide a driving apparatus which comprises an oscillating internal meshing planetary gear structure capable of great reduction in vibration and noise levels.
It is another object of the present invention to provide a driving apparatus which can achieve a reduction ratio higher than conventionals with greatly-reduced noises while suppressing an increase in size and cost as much as possible.
The foregoing objects of the present invention have been achieved by the provision of a driving apparatus comprising: an oscillating internal meshing planetary gear unit having an internal gear and an external gear making internal contact with the internal gear, the center of the internal gear lying inside the periphery of the external gear; and an external unit coupled to the oscillating internal meshing planetary gear unit so as to be capable of inputting (or extracting) power thereto (or therefrom). Between the oscillating internal meshing planetary gear unit and the external unit is interposed a frictional transmission unit for transmitting rotational power between the oscillating internal meshing planetary gear unit and the external unit by means of friction among a plurality of friction rollers making contact with each other. The friction roller unit is constituted by a simple planetary roller mechanism including the friction rollers consisting of a sun roller, a plurality of planetary rollers being retained by a planetary carrier and making rolling contact with the outer periphery of the sun roller, and a ring roller with which the plurality of planetary rollers make internal contact.
The essence of this driving apparatus consists of two points. One is that a frictional transmission unit is interposed between the oscillating internal meshing planetary gear unit and the external unit. The other is that a simple planetary roller mechanism is adopted for the frictional transmission unit.
It will become apparent from the following descriptions and test results that the present invention offers its inherent effect (beyond the bounds of common knowledge) only after the above-mentioned two points are combined with each other. In other words, either of the points by itself cannot offer such a beneficial effect.
Hereinafter, descriptions thereof will be given in further detail.
In this driving apparatus, initially, the frictional transmission unit of simple planetary roller structure is interposed between the oscillating internal meshing planetary gear unit and the external unit, and therefore the oscillating internal meshing planetary gear unit is low in input rotational speed in the first place. This allows reduction of the vibrations generated in the oscillating internal meshing planetary gear unit. In addition, the vibrations being transmitted between the units on both sides of the frictional transmission unit (in particular, the vibrations along the direction of rotation and the vibrations along the axial direction) can be absorbed by the contact surfaces of the friction rollers in the frictional transmission unit.
As a result, the complex resonance phenomena resulting from the vibration transmission between the oscillating internal meshing planetary gear unit and the external unit can be avoided to reduce the level of the noises produced by the entire driving apparatus.
Put another way, since a third unit (the frictional transmission unit), which may be regarded as a detour circuit for blocking the vibration transmission, is deliberately interposed between the oscillating internal meshing planetary gear unit and the external unit, it becomes possible to effectively suppress both the vibration transmissions from the oscillating internal meshing planetary gear unit to the external unit and from the external unit to the oscillating internal meshing planetary gear unit, with the result of overall noise reduction.
Here, what is important is that a simple planetary roller mechanism is adopted for the frictional transmission unit.
More specifically, the simple planetary roller mechanism employed here for the frictional transmission unit carries out the rotational power transmission by means of the friction among the contact surfaces of rollers, particularly owing to the power transmission structure peculiar to the simple planetary roller mechanism which involves rotations and revolutions of the planetary rollers. Therefore, the respective contact surfaces and the portions in which the planetary carrier supports the planetary rollers can absorb the vibrations (in particular, those along the direction of rotation and those along the axial direction) under the mutual transmission between the units on both sides of the frictional transmission unit (namely, the oscillating internal meshing planetary gear unit and the external unit).
The above-mentioned driving apparatus of power-distributed shaft type shown in FIG. 23 did use friction rollers as well. However, the power-distributed shaft type did not have the simple planetary roller mechanism, but a structure in which the power-distributed rollers 512 sandwiched between the sun roller 511 and the press-contact ring 513 were inherently apt to pick up vibrations of the power-distributed shafts 503. Accordingly, with the vibrations and flexure of the power-distributed shafts 503, the power-distributed rollers 512 made position shifts and vibrations to preclude the proper power transmission (without speed fluctuations) with the sun roller 511. The result was that the vibrations of the power-distributed rollers 512 themselves affected the overall vibrations and noises before the rollers 512 fulfilled their vibration absorbing function over the frictional contact surfaces.
In other words, this apparatus was not originally based on the philosophy of resonance avoidance. Therefore, the apparatus had such a configuration that the vibrations from the power-distributed shaft 503 were directly transmitted to the power-distributed rollers 512 and then to the sun roller 511, and lacked a structure for achieving the object of the present invention to avoid resonance by suppressing vibration transmission.
On this account, even the incorporation of the friction rollers did not help achieve a noise-improving effect as profound as would renew the common knowledge of geared motors. This ended up with a belief that xe2x80x9cfriction rollers can only offer such an effect at best,xe2x80x9d and the development was discontinued without further scrutiny.
On the contrary, in the case of the present invention in which a simple planetary roller mechanism is adopted for the frictional transmission unit, the power transmission is carried out by means of relative movements among the three parties, namely, the sun roller at the inner side, the ring roller at the outer side, and the planetary rollers interposed therebetween (instead of the direct power transmission by means of the power-distributed rollers"" rotations themselves). On this account, the frictional transmission unit need not undergo unnecessary deformation or vibrations from the oscillating internal meshing planetary gear unit directly.
Hence, even though interposed between the sun roller and the ring roller, the planetary rollers make only rolling contact with the sun and ring rollers at a pressure necessary for frictional transmission. The frictional contact surfaces are small in pressure fluctuation. As a result, the vibration transmission through the frictional transmission unit is suppressed. In addition, the frictional contact surfaces effectively fulfill their vibration absorbing function as described before to block the mutual vibration transmission among the units, thereby offering a high effect for noise reduction. The adoption of the simple planetary roller mechanism also permits the input and output portions of the frictional transmission unit to be arranged coaxially with each other. Thus, for example, the coupling portion between the sun roller and the external unit and the coupling portion between the planetary carrier and the oscillating internal meshing planetary gear unit can be arranged on the same axis.
This coaxiality particularly means a structure in which the aforementioned loads from the external gears are exerted exclusively on the single shaft at the central portion of the unit (unlike the power-distribution shaft type). The coaxiality is therefore beneficial in that simply increasing the rigidity of the central portion can enhance the rigidity of the entire unit. It is also beneficial in terms of vibration block because the vibrations from the external gears can be concentrated on the single, high-speed shaft, and coupling this high-speed shaft to an end of the frictional transmission unit can complete the connection with the frictional transmission unit.
In other words, the simple, compact structure not only is capable of enhancing the rigidity to beneficially allow higher torque transmission by that much, but also is advantageous in terms of noise reduction.
This coaxiality is also beneficial in making the present invention readily applicable to a geared motor in which the drive shaft of its external unit and the input and output shafts of its oscillating internally meshing planetary gear unit are aligned on a single center axis. For example, the driving apparatus of the present invention can be easily realized by adding a frictional transmission unit of the above-described simple planetary roller mechanism type to between the motor unit 3 and the oscillating internal meshing planetary gear unit 2 of the conventional geared motor 1 shown in FIG. 22. In the geared motor 1 in FIG. 22, the motor shaft 61 and the first shaft 11 of the oscillating internal meshing planetary gear unit 2 were coupled by the coupling 70. This coupling 70 may be diverted to couple the carrier of the simple planetary roller mechanism and the oscillating internal meshing planetary gear unit or to couple the shaft of the sun roller and the drive shaft of the external unit.
In addition, the adoption of the simple planetary roller mechanism makes it possible to obtain a given reduction ratio at this stage. Thus, the simple planetary roller mechanism at the preceding stage can be combined with the oscillating internal meshing planetary gear unit at the subsequent stage to achieve higher reduction ratios easily. Unlike gears, the simple planetary roller mechanism is easy to set the reduction ratio finely. This allows easy provision of a series of geared motors with many steps of reduction ratios, or a geared motor having a particular reduction ratio corresponding to a specific application.
Here, the torque transmission by means of frictional transmission at the preceding stage cannot secure as much transmission torque as the torque transmission by means of gear meshing at the subsequent stage does. This, however, makes little difference because of the following two reasons. First, the amount of torque to transmit in the preceding-stage reduction is inherently rather small. Second, the simple planetary roller mechanism, as described later, is adjustable in the torque for each roller to transmit by choosing the input and output members.
In particular, the simple planetary roller mechanism can support its planetary rollers by using a planetary carrier which is separate from the members of the oscillating internal meshing planetary gear unit. Accordingly, even when the oscillating internal meshing planetary unit undergoes some vibrations and deformation, little influence reaches the roller contact surfaces of the simple planetary roller mechanism. This realizes the torque transmission with reliability and stability, further reducing the possibility of problems arising.
Now, the driving apparatus of the present invention may be used with an external unit connected to either the high- or low-speed shaft side of the oscillating internal meshing structure, or to both. Since the highest vibrations are generated at the high-speed shaft side, the present invention is particularly effectively applied with an external unit connected to the high-speed shaft side.
The external units include machines to be driven, aside from drive sources such as a motor. The following are examples of the unit connection.
In the case where the oscillating internal meshing planetary gear unit is used as reduction gears, its high-speed shaft side is coupled with a motor as the drive source, and its low-speed shaft side is coupled with a machine to be driven. This is the typical usage of a geared motor. In the case where the oscillating internal meshing planetary gear unit is used as step-up gears, the low-speed shaft side is coupled with the drive source and the high-speed shaft side is coupled with the machine to be driven. Then, the present invention is applied to between units that may produce resonance.
Specifically, when resonance may occur between the drive source and the oscillating internal meshing planetary gear unit in mutual coupling, the frictional transmission unit is interposed between the drive source and the oscillating internal meshing planetary gear unit. When resonance may arise between the machine to be driven and the oscillating internal meshing planetary gear unit, the frictional transmission unit is interposed between the machine to be driven and the oscillating internal meshing planetary gear unit. By so doing, the overall vibrations and noises can be reduced.
The frictional transmission unit accomplishes the power transmission by means of the friction among the friction rollers. Thus, a desired reduction ratio can be obtained from this unit by properly modifying the diameters of the friction rollers contacting one another. Frictional transmission, however, is not suitable for high torque transmission. Therefore, this unit is favorably used, e.g., for the preceding-stage reduction mechanism in the cases where the oscillating internal meshing planetary gear unit is operated for speed reduction. By so doing, the overall, total reduction ratio can be set at higher levels.
Now, the ways to support the planetary rollers in the aforementioned simple planetary roller mechanism includes the following two.
In one way, the planetary carrier in the simple planetary roller mechanism is provided with a retainer for occupying spaces around the plurality of planetary rollers to retain the planetary rollers at constant mutual positions (hereinafter, referred to as retainer type).
In the other, the planetary carrier in the simple planetary roller mechanism is provided with pins for penetrating through the respective centers of the planetary rollers to retain the planetary rollers at constant mutual positions (hereinafter, referred to as pin type).
As for the differences between the retainer type and the pin type, the pin type is superior to the retainer type in: (a) power transmission efficiency, (b) power transmission stability, and (c) allowance for torsion and mounting errors. The reason for this is that the pin type has a structure of fitting the planetary rollers on the outer peripheries of the pins via bearings so that it is easy for the planetary rollers to maintain higher rotational performance than in the retainer type.
In addition, the effects (a)-(c) suggest that the pin type also generally offers more favorable properties as to xe2x80x9cthe vibration suppressing effectxe2x80x9d for a long term as compared to the retainer type.
However, as far as xe2x80x9cthe vibration suppressing effectxe2x80x9d is concerned, there is a possibility of making the retainer type offer a better effect than the pin type does, depending on the design and maintenance. The reason for this seems to be that the retainer type, as described later, has the output-extracting retainer which is kept out of press contact with the sun roller and the ring roller, or put in a sort of free state, to exclusively receive circumferential driving forces from the planetary rollers. This retainer structure makes it possible to avoid the vibration transmissions through the following two paths:
a) pins (oscillating-internal-meshing-planetary-gear-unit side)xe2x86x92planetary rollersxe2x86x92sun roller (motor side); and
b) pins (oscillating-internal meshing-planetary-gear-unit side)xe2x86x92planetary rollersxe2x86x92ring roller (casing side).
Accordingly, vibrations can be intercepted between the oscillating internal meshing planetary gear unit and the external unit with yet higher reliability.
The relationship among the fixed, input, and output elements of the simple planetary roller mechanism creates the possible combinations shown in the table of FIG. 16. To name the combinations:
1) With the sun roller as the input element, the ring roller makes the fixed element and the planetary carrier the output element, or the ring roller makes the output element and the planetary carrier the fixed element;
2) With the planetary carrier as the input element, the ring roller makes the fixed element and the sun roller the output element, or the ring roller makes the output element and the sun roller the fixed element; and
3) With the ring roller as the input element, the planetary carrier makes the fixed element and the sun roller the output element, or the planetary carrier makes the output element and the sun roller the fixed element.
The simple planetary roller mechanism prefers that the ring roller make the fixed element, either the planetary carrier for supporting the plurality of planetary rollers or the sun roller the input element, and the remaining the output element.
When the fixed element is thus made of the ring roller arranged on the periphery, this ring roller has only to be fixed to the casing, thereby allowing rather simple configuration for the mechanism.
It is also preferable that: the above-mentioned external unit be a motor unit for supplying a rotational input to the oscillating internal meshing planetary gear unit; the frictional transmission unit be interposed between a drive shaft of the motor unit and the oscillating internal meshing planetary gear unit; and the oscillating internal meshing planetary gear unit and the motor unit be integrally connected with each other by a joint casing comprising parts of the casings for these units, the frictional gearing unit being arranged inside the joint casing.
Given that the external unit is a motor unit, the drive shaft of the motor unit is connected to the high-speed shaft side of the oscillating internal meshing planetary gear unit when the planetary gear unit is used as reduction gears. In short, there is constituted a typical geared motor. Then, in such a geared motor, the vibration amplifying effect resulting from resonance can be avoided by interposing the frictional transmission unit between the high-speed shaft of the oscillating internal meshing planetary gear unit and the drive shaft of the motor unit to block the vibration transmission between the motor unit and the oscillating internal meshing planetary gear unit.
By the way, in typical composition of a geared motor, the casing of the oscillating internal meshing planetary gear unit and the casing of the motor unit are coupled with each other to form an integrated geared motor. In conventional cases, both the units are coupled via a joint casing that comprises a part of the casing of each unit (see Japanese Patent Laid-Open Publication No.Hei 5-231482).
Therefore, the newly-added frictional transmission unit can be arranged inside that joint casing to permit its easy incorporation without a significant change in the structures of the units on both sides.
Of the coupling portions between the frictional transmission unit and the oscillating internal meshing planetary gear unit and between the frictional transmission unit and the external unit, at least one coupling portion preferably has a floating connection structure.
According to this constitution, the shaft coupling portion of the frictional transmission unit with the oscillating internal meshing planetary gear unit or the external unit has a floating connection structure. Therefore, the vibrations caused by each unit""s oscillations can be prevented from acting on the frictional rollers via the coupling portion, thereby suppressing fluctuations in the contact pressure between the friction rollers. This permits the stable, sure torque transmission with no fluctuations in transmission torque in the frictional transmission unit.
Here, it is yet preferable that: of the coupling portions between the planetary carrier in the frictional transmission unit of simple planetary roller mechanism and the oscillating internal meshing planetary gear unit and between the sun roller and the external unit, at least the coupling portion between the planetary carrier and the oscillating internal meshing planetary gear unit has the floating connection structure.
Specifically, according to this constitution, at least the coupling portion between the planetary carrier and the oscillating internal meshing planetary gear unit is provided with the floating structure to minimize the transmission of radial vibrations from the oscillating internal meshing planetary gear unit to the single planetary roller mechanism in the case where the ring roller of the simple planetary roller mechanism makes the fixed element, the planetary carrier is coupled to the oscillating internal meshing planetary gear unit, and the sun roller is coupled to the external unit. Consequently, further suppression of the mutual vibration transmission between the oscillating internal meshing planetary gear unit and the external unit can be achieved to avoid the resonance problem.
The above-mentioned floating connection structure may employ a spline connection structure, for example. This facilitates the realization of the structure, for a floating connection state can be obtained from the splines, a commonly available shaft-coupling structure.
Incidentally, other examples of the floating connection structure include a gear connection.
As described above, the relationship among the fixed, input, and output elements in a simple planetary roller mechanism have the combinations shown in FIG. 16. Of these, the constitutions in which the ring roller of the single planetary roller mechanism makes the fixed element with either the planetary carrier supporting the plurality of planetary rollers or the sun roller as the input element and the remaining as the output element (the constitutions corresponding to A and C in FIG. 16) particularly provide various advantages when combined with the assembly that utilizes a structure of forming a mounting reference surface.
That is, when the fixed element is made of the ring roller arranged on the periphery, it is possible to fix this ring roller of greatest dimension to the casing. This basically allows simpler structures for both the simple planetary roller mechanism and the casing, and achieves further noise reduction.
The structure of forming a mounting reference surface is preferably adopted due to the following reason.
In its process of contrivance, the driving apparatus according to the present invention used common assembling means to fix the ring roller to the casing. Specifically, a cylindrical accommodating portion having an inside diameter somewhat smaller than the outside diameter of the ring roller was formed in the casing, and the ring roller was xe2x80x9cpress-fittedxe2x80x9d and fixed to the accommodating portion. However, tests revealed that the method of fixing the ring roller by xe2x80x9cpress-fitxe2x80x9d had a considerable number of problems. The reason for this seems to be as follows:
(1) In view of miniaturization, the ring roller needed to have a thickness as small as possible. When such a ring roller was subjected to the method of fixing by pressing, the ring roller might be deformed radially inwardly. This radially inward deformation could produce fluctuations in contact pressure (line pressure) both on the contact surfaces between the planetary rollers and the ring roller and on the contact surfaces between the planetary rollers and the sun roller. As a result, the value of the contact pressure (line pressure) after actual mounting of the ring roller differed from the value of the contact pressure predetermined before the incorporation. In particular, the actual pressure fluctuated in accordance with circumferential positions, thereby precluding smooth rotations/revolutions of the planetary rollers.
(2) Under the circumstances where the high-rigidity casing exerted high pressures on the ring roller from radial outsides, the majority of the radial vibrations having been transmitted to the planetary rollers (through the sun roller or the planetary carrier) were transmitted as-received to the mating side through the planetary carrier or the sun roller.
In other words, the ring roller under the press-fitted state had little allowance in bending (distorting) itself slightly in the radial direction. Thus, in this driving apparatus (under the process of contrivance) having the ring roller fixed by press-fit, the majority of the radial vibrational energy having been received by the planetary rollers via the planetary carrier was xe2x80x9cdirectlyxe2x80x9d transmitted to the sun roller while the majority of the radial vibrational energy having been received by the planetary rollers via the sun roller was xe2x80x9cdirectlyxe2x80x9d transmitted to the planetary carrier. In particular, a so-called xe2x80x9ctransmission structure for radial vibrational energyxe2x80x9d was formed in the simple planetary roller mechanism.
(3) The vibrations having been transmitted to the ring roller were then transmitted to the casing with a high possibility of vibrating the casing.
That is, after the fixing by press-fit, the vibrations having been transmitted to the ring roller would directly vibrate the cylindrical surface of the roller in radial directions (the direction of the thickness) against the casing of generally cylindrical shape. Accordingly, the casing could easily cause resonance, which was transmitted to the casings of the external unit and the internal meshing planetary gear unit to induce resonance of the entire driving apparatus.
However, when the press-fit fixing is abandoned and substituted with the assembly by using a mounting reference surface, the mounting deformation of the ring roller resulting from the press-fit can be minimized to maintain the uniformity and stability of the tangential line pressures. At the same time, vibrations of the ring roller itself can be allowed to some extent to achieve energy absorption there. In addition, these vibrations can be surely received by the mounting reference surface (of higher rigidity in the radial direction) formed along the direction of the casing""s thickness (or by a surface conforming thereto, to be described later) so that the vibrations are prevented from being transmitted directly in the direction of the casing""s thickness.
In other words, the ring roller can be fixed to the casing without undergoing radial pressures, or as pressed against the mounting reference surface perpendicular to the axial direction, to realize smooth rotations/revolutions of the planetary rollers. Moreover, the ring roller""s capacity for radial deformation can provide a radial vibration absorbing function to the ring roller itself and minimize vibrations of this ring roller being transmitted to the casing side, thereby achieving further noise reduction.
This type of method for fixing the ring roller is highly advantageous in terms of noise suppression, as described previously. In addition to this simple noise reduction, the method also eliminates the need for the process of press-fitting the ring roller, thereby improving the assembling efficiency.
Here, the ring roller may be configured to be adjustable in axis position within the mounting reference surface. In such a configuration, the axis of the ring roller can be readily adjusted to coincide with the axes of the respective power transmission shafts of the oscillating internal meshing planetary gear unit and external unit to which the frictional transmission unit is coupled. This allows quicker, easier assembly of the frictional transmission unit. More specifically, when the ring roller was mounted by press-fit, the axis adjustment (alignment) was impossible unless the oscillating internal meshing planetary gear unit and the external unit were displaced. On the other hand, when the ring roller is free from radial pressures and is provided with enough spaces for radial displacement as in the present invention, the axis is easy to adjust, and therefore assembling efficiency is improved dramatically.
Moreover, in order to draw the best out of the coaxiality which is the merit of the present invention, the sun roller may be provided with a sun-roller-side shaft insertion hole into which a power transmission shaft of the external unit is insertable, and the planetary carrier is provided with a carrier-side shaft insertion hole into which a power transmission shaft of the oscillating internal meshing planetary gear unit is insertable, so as to form the frictional transmission unit into a shaft coupling structure for allowing relative rotations of the power transmission shafts.
Such constitution is highly advantageous in the following aspect. That is, the coaxiality between the input and output elements of the simple planetary roller mechanism makes the present invention easily applicable to a geared motor that has a now-commonly-known structure in which the drive shaft of the external unit and the input and output shafts of the oscillating internal meshing planetary gear unit are aligned on a single center axis and these units are coupled with each other by an ordinary coupling.
For example, in the conventional geared motor 1 as shown in FIG. 22, the motor shaft 61 of the motor unit 3 and the first shaft 11 of the oscillating internal meshing planetary gear unit 2 are coupled with each other by a common coupling (shaft coupling). Geared motors of such structure are not limited to that shown in FIG. 22. Most of the conventional driving apparatuses containing an oscillating internal meshing planetary gear unit and an external unit have similar structures. Under such circumstances, the frictional transmission unit provided with the xe2x80x9cshaft coupling structurexe2x80x9d by forming shaft insertion holes in the carrier and sun roller can be employed and replaced with the ordinary coupling to easily realize the driving apparatus of the present invention with only slight changes in design. Moreover, the simple planetary roller mechanism can be realized into an axially compact configuration, causing no axial extension of the entire driving apparatus.
In particular, the application of the xe2x80x9cshaft coupling structurexe2x80x9d to a frictional transmission unit is combined with the adoption of a mounting reference surface to allow the frictional transmission unit to be replaced by another frictional transmission unit of different reduction ratio, with almost the same trouble as that required in replacing ordinary couplings. Therefore, it becomes possible to flexibly adapt this driving apparatus to user demands for a wide range of reduction ratios. Here, what needs to be replaced is the frictional transmission unit alone; therefore, the replacement costs less as compared to the replacement of the entire geared motor.
In the frictional transmission unit of xe2x80x9cshaft coupling structure,xe2x80x9d at least either the sun-roller-side shaft insertion hole or the carrier-side shaft insertion hole is formed into a floating connection structure with respect to the power transmission shaft inserted therethrough. This realizes the aforementioned floating connection structure on the shaft coupling portion of the frictional transmission unit with the oscillating internal meshing planetary gear unit or the external unit.
In particular, the ring roller of this frictional transmission unit is fixed to the casing on the basis of the mounting reference surface. Therefore, unlike ordinary couplings which are simply fitted onto shafts to keep their own positions (by being supported by the shafts in return), such as those shown in FIGS. 22 and 23, this frictional transmission unit can keep its own position independent of the power transmission shafts. As a result, each power transmission shaft and the corresponding shaft insertion hole can maintain a constant clearance therebetween all the time, further ensuring the blockage of vibrations and noises. Given that this frictional transmission unit is adjustable in axis, the clearances can also be set precisely from the beginning. This combines with the maintenance of constant clearances to achieve further suppression of noises and vibrations.
In a concrete method for fixing the ring roller to the casing, the ring roller is provided with a bolt hole piercing therethrough in the direction of the rotation axis so that the ring roller is fixable to the mounting reference surface by a fixing bolt inserted through the bolt hole and threadedly engaged with a tapped hole formed in the mounting reference surface. Here, the bolt hole has a diameter somewhat greater than that of the fixing bolt so that the ring roller is adjustable in axis position within the mounting reference surface as long as the fixing bolt is fitted to the bolt hole with play.
This allows the ring roller to be surely fixed by the most common means, or bolts, with no particular increase in manufacturing costs. Besides, since the axis position of the ring roller can be adjusted by the simpler method, suppression in cost is possible and the assembly is facilitated.
Furthermore, the planetary carrier of the simple planetary roller mechanism may be provided with pins which penetrate through center holes formed at the rotational centers of the respective planetary rollers to retain the planetary rollers at constant mutual positions. Then, an inner roller of generally cylindrical shape is inserted to the clearance between the outer peripheral surface of each pin and the inner peripheral surface of the corresponding center hole so that the inner roller makes sliding rotation with respect to both the peripheral surfaces.
In such constitution, the inner rollers can make rotations while sliding over the outer peripheral surfaces of the pins and the inner peripheral surfaces of the planetary rollers, to absorb the difference in rotational speed between the pins and the planetary rollers. More specifically, the inner rollers inserted to between the pins and the planetary rollers make rotations at a speed intermediate between the revolving speed of the pins and the rotating speed of the planetary rollers. Therefore, as compared to the case where the pins and the planetary rollers are in xe2x80x9cdirectxe2x80x9d contact with each other, the inner and outer contact surfaces of the inner rollers slide at a speed differential smaller than the actual difference in rotational speed between the pins and the planetary rollers. This consequently allows reductions of frictional heat generation, frictional resistance, and the like.
The inner rollers also offer superior strength as compared to needle rollers, thereby enhancing the durability in long run and high-speed rotations.
The present invention has been described so far in terms of inter-unit coupling. As described below, another aspect of the present invention consists in a driving apparatus separated from external units.
That is, the present invention may also be regarded as comprises: a rotating shaft (214, 414 in the embodiment) to be connected to an external unit; an oscillating internal meshing planetary gear mechanism having an internal gear and an external gear making internal contact with the internal gear, the center of the internal gear lying inside the periphery of the external gear; and a frictional transmission unit of simple planetary roller mechanism, having friction rollers consisting of a sun roller, a plurality of planetary rollers being retained by a planetary carrier and making rolling contact with the outer periphery of the sun roller, and a ring roller having the planetary rollers arranged inside so as to make internal contact. Here, one of the sun roller, planetary carrier, and ring roller is fixed. Either of the other two is coupled to the oscillating internal meshing planetary gear mechanism. The remaining one is coupled to the rotating shaft.
Again, it is preferable that: the ring roller is fixed, the planetary carrier is coupled to the oscillating internal meshing planetary gear mechanism, and the sun roller is coupled to the rotating shaft. Of the coupling portions between the planetary carrier and the oscillating internal meshing planetary gear mechanism and between the sun roller and the rotating shaft, at least one coupling portion preferably has a floating connection structure.
For the above-mentioned oscillating internal meshing planetary gear mechanism, an oscillating internal meshing planetary gear mechanism may be adopted which has a first shaft and a second shaft located on the center axis of the driving apparatus. Here, an external gear is fitted on the outer periphery of the first shaft via an eccentric body so as to be capable of oscillating rotations with respect to the first shaft. An internal gear with which the external gear meshes internally is provided concentrically with the first shaft. The second shaft is coupled to the external gear via means for extracting only the rotational component of the external gear.
Incidentally, focusing attention on the combination of xe2x80x9ca frictionally-engaging unit and a floating connectionxe2x80x9d can also result in a frictional transmission unit 2300 as shown in FIG. 21, for example. In the diagram, the reference numeral 2301 represents the input-side shaft to be connected to a motor shaft 2161 via a floating connection portion F1, the numeral 2302 an input-side roller arranged on the shaft 2301, the numeral 2303 the output-side shaft to be connect to a first shaft 2111 of a reduction gear unit 2102 via a floating connection portion F2, and the numeral 2304 an output-side roller arranged on the shaft 2303. The reference numeral 2305 represents the idle shaft arranged in parallel to the aforementioned input- and output-side shafts 2301 and 2303. On this shaft 2305 are arranged first idle roller 2306 and second idle roller 2307 coming into contact with the aforementioned input- and output-side rollers 2302 and 2304, respectively.
This frictional transmission unit 2300 transmits rotations of the motor shaft 2161 in such order that: floating connection portion F1xe2x86x92input-side shaft 2301xe2x86x92input-side roller 2302xe2x86x92first idle roller 2306xe2x86x92idle shaft 2305xe2x86x92second idle roller 2307xe2x86x92output-side roller 2304xe2x86x92output-side shaft 2303xe2x86x92floating connection portion F2xe2x86x92first shaft 2111.
At first glance, the frictional transmission unit 2300 and the floating connections in combination appear to offer a noise reduction effect. And this configuration indeed produced some effect. However, the noise reducing effect produced was not as xe2x80x9cdramaticxe2x80x9d as that of the present invention.
Now, the following is one of the constitutions effective for the most rational realization of the present invention.
That is, a driving apparatus comprising a drive unit for generating rotational power, a first reduction mechanism unit coupled to an output shaft of the drive unit to transmit the rotational power, and a second reduction mechanism unit of support carrier transmission type, including reduction gears to be coupled to the first reduction mechanism unit, and a pair of support carriers rotatably supported by a casing at both axial outsides of the reduction gears via bearings, the support carriers for extracting rotational power of the reduction gears, wherein: the above-mentioned first reduction mechanism unit has a simple planetary roller structure of friction transmission type, including a sun roller to be coupled to a drive shaft of the drive unit, a planetary roller making rolling contact with the outer periphery of the sun roller, a ring roller with which the planetary roller makes internal contact, and a planetary carrier for extracting the revolution component of the planetary roller and transmitting the same to an input shaft of the second reduction mechanism unit, the outside diameter of the ring roller being set within the outside diameter of the bearing supporting the drive-unit-side support carrier of the pair of support carriers in the second reduction mechanism unit; and the above-described ring roller is situate within the casing, in a space on the drive-unit side of the bearing.
In short, the first reduction mechanism unit serving as the preceding reduction side of the driving apparatus is constituted as a simple planetary roller mechanism of frictional transmission type, and the outside diameter of the ring roller in the first reduction mechanism unit is set within the outside diameter of the bearing in the second reduction mechanism unit. This makes it possible to couple the first and second reduction mechanism units to each other with a highly compact configuration.
When this constitution is adopted, the space within the casing, on the drive-unit side of the bearing can be so expanded as to accommodate the simple planetary roller mechanism, with only an extremely simple change in design (namely, just a little extension of the casing). Moreover, this expanded space has little effect on the size of the entire driving apparatus.
Setting the outside diameter of the ring roller within that of the above-mentioned bearing makes the ring roller mountable to the casing from the side opposite to the drive unit (with the bearing detached), i.e., from the side closer to the second reduction mechanism unit to be mounted later. This greatly simplifies the internal configuration of the casing, and significantly facilitates the manufacture and assembly of the apparatus (the manufacturing and other methods will be described later).
Accordingly, it becomes possible to arrange the first reduction mechanism unit of simple planetary roller mechanism into the space on the drive-unit side of the bearing, within the same casing as that containing the second reduction mechanism unit. Therefore, the first and second reduction mechanism units can be combined with each other to achieve reduction ratios high enough to meet the market needs while greatly decreasing the axial dimension and reducing the manufacturing costs as compared to the conventional ones. Obviously, the driving apparatus constituted as described above can output the power of the drive unit without losing the coaxiality. The driving apparatus undergoes no increase in radial dimension.
Furthermore, this driving apparatus can realize the inherent, as-provided effects of the present invention. That is, the first reduction mechanism unit, because of being a frictional transmission type, is capable of quiet operation. In addition, both the first and second reduction mechanism units can be accommodated in a single casing. Therefore, the resonance and other phenomena conventionally caused by the internal spaces of two casings can be suppressed. Moreover, since the vibration transmission between the drive unit (motor) and the second reduction mechanism unit is blocked due to the presence of the first reduction mechanism unit of frictional transmission type, the resonance in the respective units is lowered and operational noises are reduced. The result is that the three requirements having been regarded as difficult to meet, i.e., a high reduction ratio, a compact configuration, and quietness, can be satisfied rationally.
Constituting the driving apparatus as described above also achieves a considerable simplification of the manufacturing steps. The concrete manufacturing method comprises the steps of: mounting the drive unit on the casing; attaching the first reduction mechanism unit to this casing with the drive unit mounted thereon, from the side opposite to the drive unit; and attaching the second reduction mechanism unit to the casing with the first reduction mechanism unit attached thereto.
This manufacturing method is highly labor-saving because the first and second reduction mechanism units (coaxial with each other) can be sequentially built in with reference to the drive shaft of the drive unit which has been fixed to the casing initially.
In particular, the simple planetary roller structure adopted for the first reduction mechanism unit and the oscillating internal meshing planetary gear structure adopted for the second reduction mechanism unit, both are high in modularity. Therefore, these units can be independently assembled to some extent before built into the casing together. Moreover, both the structures are intended for coaxial transmission of the rotational power, they facilitate the positioning and permit quick assembly.
In terms of the assembly facilitation, it is preferable that both the coupling structures between the output shaft of the drive unit and the sun roller of the first reduction mechanism unit and between the planetary carrier of the first reduction mechanism unit and the first shaft of the second reduction mechanism unit have a spline connection structure for allowing axial play. By this means, the first and second reduction mechanism units hardly require fine-adjustment in their mounting steps, and thus can be assembled still more easily and quickly.
The second reduction mechanism unit of this driving apparatus essentially has a support carrier transmission type structure, which includes a speed reducer to be coupled to the first reduction mechanism unit, and a pair of support carriers rotatably supported by the casing at both axial outsides of the speed reducer via bearings to extract the rotational power of the speed reducer. As a matter of course, even an oscillating internal meshing planetary gear structure of support carrier transmission type is similarly applicable to the second reduction mechanism unit. This constitution may also be combined with the above-described constitution for the xe2x80x9cmounting reference surface.xe2x80x9d
The nature, principle, and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings in which like parts are designated by like reference numerals or characters.